U.S. patent number 8,962,511 [Application Number 12/967,262] was granted by the patent office on 2015-02-24 for synthetic catalysts that separate co.sub.2 from the atmosphere and gas mixtures.
This patent grant is currently assigned to Lawrence Livermore National Security, LLC. The grantee listed for this patent is Roger D. Aines, Edmond Y. Lau, Felice C. Lightstone, Joe H. Satcher, Jr., Sergio E. Wong. Invention is credited to Roger D. Aines, Edmond Y. Lau, Felice C. Lightstone, Joe H. Satcher, Jr., Sergio E. Wong.
United States Patent |
8,962,511 |
Lightstone , et al. |
February 24, 2015 |
Synthetic catalysts that separate CO.sub.2 from the atmosphere and
gas mixtures
Abstract
The creation of a catalyst that can be used for a wide variety
of applications including the steps of developing preliminary
information regarding the catalyst, using the preliminary
information to produce a template of the catalyst, and using the
template of the catalyst to produce the catalyst.
Inventors: |
Lightstone; Felice C. (Fremont,
CA), Wong; Sergio E. (Campbell, CA), Lau; Edmond Y.
(Dublin, CA), Satcher, Jr.; Joe H. (Patterson, CA),
Aines; Roger D. (Livermore, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lightstone; Felice C.
Wong; Sergio E.
Lau; Edmond Y.
Satcher, Jr.; Joe H.
Aines; Roger D. |
Fremont
Campbell
Dublin
Patterson
Livermore |
CA
CA
CA
CA
CA |
US
US
US
US
US |
|
|
Assignee: |
Lawrence Livermore National
Security, LLC (Livermore, CA)
|
Family
ID: |
44151656 |
Appl.
No.: |
12/967,262 |
Filed: |
December 14, 2010 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20110151537 A1 |
Jun 23, 2011 |
|
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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61287375 |
Dec 17, 2009 |
|
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Current U.S.
Class: |
502/174 |
Current CPC
Class: |
C12P
7/04 (20130101); B01D 53/1475 (20130101); B01D
53/1493 (20130101); B01D 53/62 (20130101); C12N
9/0073 (20130101); B01D 53/86 (20130101); Y02C
20/40 (20200801); Y02P 20/152 (20151101); B01D
2252/60 (20130101); Y02C 10/04 (20130101); Y02C
10/06 (20130101); B01D 2255/20792 (20130101); Y02P
20/59 (20151101); B01D 2255/20746 (20130101); B01D
2257/504 (20130101); Y02C 20/20 (20130101); B01D
2255/20761 (20130101); B01D 2258/06 (20130101); B01D
2258/0283 (20130101); Y02P 20/151 (20151101) |
Current International
Class: |
B01J
21/18 (20060101) |
Field of
Search: |
;502/300 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Mayes; Melvin C
Assistant Examiner: Vaden; Kenneth
Attorney, Agent or Firm: Scott; Eddie E.
Government Interests
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH AND DEVELOPMENT
The United States Government has rights in this invention pursuant
to Contract No. DE-AC52-07NA27344 between the United States
Department of Energy and Lawrence Livermore National Security, LLC
for the operation of Lawrence Livermore National Laboratory.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims benefit under 35 U.S.C. .sctn.119(e)
of U.S. Provisional Patent Application No. 61/287,375 filed Dec.
17, 2009 entitled "Synthetic Catalysts that Separate CO.sub.2 from
the Atmosphere and Gas Mixtures," the disclosure of which is hereby
incorporated by reference in its entirety for all purposes.
Claims
The invention claimed is:
1. A method of producing a catalyst for harvesting carbon dioxide
from a gas mixture, comprising the steps of: developing preliminary
information regarding the catalyst for harvesting carbon dioxide
from the gas mixture wherein said preliminary information includes
potential energy surfaces around a metal center that will optimize
reaction with carbon dioxide, said step of developing preliminary
information regarding the catalyst for harvesting carbon dioxide
from a gas mixture including using molecule mimics wherein said
molecule mimics are 1,4,7,10-tetraacyclododedacane and
1,5,9-triazacyclododedacane, using said preliminary information for
generating a selection of linking atoms that compose a scaffold on
said metal center that will optimize reaction with carbon dioxide,
and using said preliminary information and said selection of
linking atoms that compose a scaffold on said metal center to
produce the catalyst for harvesting carbon dioxide from the gas
mixture.
2. The method of producing a catalyst for harvesting carbon dioxide
from a gas mixture of claim 1 wherein said metal center is a zinc
metal center.
3. The method of producing a catalyst for harvesting carbon dioxide
from a gas mixture of claim 1 wherein said metal center is a copper
metal center.
Description
BACKGROUND
1. Field of Endeavor
The present invention relates to carbon dioxide and more
particularly to removal of carbon dioxide from the atmosphere and
gas mixtures
2. State of Technology
Direct separation of CO.sub.2 from the atmosphere is an emerging
technology option. Living creatures have already conquered this
technologically difficult reaction by catalyzing the reaction of
CO2 to CO.sub.3H-- with carbonic anhydrase. In recent years a
growing awareness of CO.sub.2 atmospheric levels sparked interest
in developing rapid ways to absorb carbon dioxide from industrial
gas streams. Most industrial separation processes for CO.sub.2
involve a liquid in which the dissolved CO.sub.2 ionizes, greatly
increasing its solubility and absorption rate. The slow step in
such processes is well known to be the formation of carbonic acid.
This reaction controls the uptake of carbon dioxide by the ocean
because it is just slow enough to cause a significant mass transfer
limitation at the water's surface. This mass transfer limitation
also applies to industrial gas separations and results in overall
decreases in rate of factors in excess of 1000.times. over that
which could be obtained if the hydration of the CO.sub.2 were not
the rate limiting step. Speeding such processes through the use of
catalysts or enzymes would permit smaller and less expensive
separation processes to remove CO.sub.2 from industrial gas
emissions, and be fast enough to permit removal of CO.sub.2 from
the atmosphere.
In recent years a growing awareness of CO.sub.2 atmospheric revels
sparked interest in. developing rapid ways to absorb carbon dioxide
from industrial gas streams. Most industrial separation processes
for CO.sub.2 involve a liquid in which the dissolved CO.sub.2
ionizes, greatly increasing its solubility and absorption rate. The
slow step in such processes is well known to be the formation of
carbonic acid. This reaction controls the uptake of carbon dioxide
by the ocean because it is just slow enough to cause a significant
mass transfer limitation at the water's surface. This mass transfer
limitation also applies to industrial gas separations and results
in overall decreases in rate of actors in excess of 1000.times.
over that which could be obtained if the hydration of the CO.sub.2
were not the rate limiting step. Speeding such processes through
the use of catalysis or enzymes would permit smaller and less
expensive separation processes to remove CO.sub.2 from industrial
gas emissions, and could even conceivably be fast enough to permit
removal of CO.sub.2 from the atmosphere.
Carbonic anhydrase (CA) efficiently catalysis the reversible
hydration of CO.sub.2 to carbonic acid. In erythrocytes, its rate
kinetics surpasses the CO.sub.2 diffusion rate out of the cell. It
is a ubiquitous enzyme expressed in prokaryote, and eukaryote
organisms. The HMM library and genome assignment server lists 33 CA
homologs in the human genome. CAII is the most efficient of the
three forms of CA. Deficiency of CAII is associated with renal
tubular acidosis and brain calcification, while it also plays a
role in bone readsorption. Since its discovery, it sparked great
interest due to its highly efficient kinetics and its Zn.sup.2+
metal center.
Current research into the use of carbonic anhydrase for industrial
CO.sub.2 capture has received limited publication partially due to
the difficulty of maintaining viable enzyme in industrial
processes. Trachtenberg et al uses a membrane-countercurrent system
originally designed for spacecraft use. Bhattacharya et al uses a
spray system with carbonic anhydrase in the spray. Azari and
Nemat-Gorgani examined means of using the reversible unfolding of
the enzyme, caused by heat, to attach it to more sturdy substrates
for industrial use. Yan et al. incorporate single carbonic anydrase
molecules in a spherical nanogel and report that greatly improved
temperature stability with only moderate loss of activity.
Applicants are investigating whether small catalytic mimelics of CA
may be more attractive as components of industrial gas separation
processes, Creating such mimetics requires knowledge of the
catalytic mechanism and possible degradation mechanisms of the
catalytic enter.
Experimental and theoretical research contributed to the current
understanding of CA's reaction mechanism. Crystallographic studies
showed the Zrt.sup.2 ion in the CAII binding site is chelated by
three hislidine side-chains and a water molecule to yield a
tetrahedral coordination geometry. The reaction is thought to occur
in three steps: 1) deprotonation of the water ligand to form an
activated hydroxyl group, 2) a nucleophilic attack from the
hydroxyl oxygen to the carbon atom in CO.sub.2 to form an
intermediate species, and 3) the displacement of bicarbonate by
water, which re-starts the cycle.
SUMMARY
Features and advantages of the present invention will become
apparent from the following description. Applicants are providing
this description, which includes drawings and examples of specific
embodiments, to give a broad representation of the invention.
Various changes and modifications within the spirit and scope of
the invention will become apparent to those skilled in the art from
this description and by practice of the invention. The scope of the
invention is not intended to be limited to the particular forms
disclosed and the invention covers all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the claims.
The present invention is the creation of a catalyst that can be
used for a wide variety of applications. In one embodiment the
present invention provides a method of producing a catalyst for
harvesting carbon dioxide from a gas mixture. The method includes
the steps of developing preliminary information regarding the
catalyst for harvesting carbon dioxide from a gas mixture, using
the preliminary information to produce a template of the catalyst
for harvesting carbon dioxide from a gas mixture, and using the
template of the catalyst for harvesting carbon dioxide from a gas
mixture to produce the catalyst for harvesting carbon dioxide from
a gas mixture.
One embodiment the present invention is the creation of a catalyst
that can sequester CO.sub.2 from the air and convert the carbon
into a water soluble form. It has been shown that Zn.sup.2+ will
work for the catalyst. Various metals have been shown to work in
carbonic anhydrase, but different metals have not been shown to
work in the small molecule catalysts. Applicants use other metals
such as cobalt, copper and iron. Applicants have also designed a
method to attach the catalyst to a surface. Applicants' compounds
are tethered to a surface to maximize the regeneration of the
catalyst.
Another embodiment the present invention is the creation of a
catalyst for conversion of methane to methanol. Yet another
embodiment the present invention is the creation of a catalyst for
water oxidizing using an oxygen evolving catalyst. Another
embodiment the present invention is the creation of a catalyst for
nitrogen fixation.
Use of the present invention includes capturing CO.sub.2 emissions
from industrial processes or vehicles or from the air. This
included enhanced technology for removing carbon dioxide from
industrial gas waste streams, natural gas, and the atmosphere.
Other uses of the present invention include conversion of methane
to methanol, water oxidizing, and nitrogen fixation
The invention is susceptible to modifications and alternative
forms. Specific embodiments are shown by way of example. It is to
be understood that the invention is not limited to the particular
forms disclosed. The invention covers all modifications,
equivalents, and alternatives falling within the spirit and scope
of the invention as defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated into and
constitute a part of the specification, illustrate specific
embodiments of the invention and, together with the general
description of the invention given above, and the detailed
description of the specific embodiments, serve to explain the
principles of the invention.
FIG. 1 illustrates the speciation of carbon dioxide in water as a
function of pH, and at a constant overall concentration of
carbon.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Referring to the drawings, to the following detailed description,
and to incorporated materials, detailed information about the
invention is provided including the description of specific
embodiments. The detailed description serves to explain the
principles of the invention. The invention is susceptible to
modifications and alternative forms. The invention is not limited
to the particular forms disclosed. The invention covers all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the claims.
Current carbon dioxide separation schemes for managing CO.sub.2
concentrations near atmospheric concentrations utilize water as the
separation media. This is because water provides an extremely large
factor to separate carbon dioxide from non-ionizable nitrogen and
oxygen. These gases are limited to solubilities of around 40 ppm in
water--but with appropriate chemical control the ionized species
bicarbonate HC03.sup.- and carbonate CO.sub.3 can have
concentrations thousands of times higher. In other words, once the
CO.sub.2 dissolves in water, it is now a very different molecule
than oxygen and nitrogen, with concordant high separation
efficiency.
The best hope for speeding up the dissolution is by quickly
reacting the CO.sub.2 to one of its other, more soluble forms
(HCO.sub.3.sup.- or CO.sub.3.sup.2-) and avoiding the limitation
imposed by the low Henry's law coefficient. Any kinetic limitation
based on liquid processes starts at the concentration at the
air-water interface--this concentration is set by Henry's law. When
the concentration on the air side doubles, the water side
concentration doubles, as does in general the mass flux of any
process in the water transferring CO.sub.2 away from the interface.
This inherently makes it difficult to design air capture processes.
For instance, using identical capture processes for air and coal
flue gas, the flue gas process will have a mass flux more than 300
times larger simply due to the increased concentration. This has an
enormous influence on process design, since prima facie it suggests
that in order to handle a similar amount of CO.sub.2, the air
capture process would have to be 300 times larger.
The speciation of carbon dioxide in water is therefore critical to
both concentration, and to the rate at which water can absorb the
gas. FIG. 1 highlights two distinct concentration regions:
Region 1. Below pH 5: dissolved carbon dioxide is low because the
unionized species predominate. Total dissolved CO.sub.2 can only be
increased by increasing the gas pressure of CO.sub.2 above the
water. This is the carbonated beverage regime--the gas comes out
when the pressure is released.
Region 2. Above pH 5: the concentration, and potentially the
transfer rate, can be increased by adding a pH buffer to the
solution that binds to the protons released which are released in
the conversions CO.sub.2(aq)+H.sub.2O
H.sub.2CO.sub.3H.sup.++HC0.sub.3.sub.-2H.sup.++CO.sub.3.sup.2-
(Equation 1)
In region (2) above pH 5, the ability of water to carry carbon is
only limited by the solubility of appropriate buffer species such
as substituted amines and strong hydroxides like NaOH.
However, the fact that a solution is capable of carrying a given
amount of carbon dioxide does not mean the uptake occurs instantly.
The initial dissolution step at below pH 8 involves the gas
dissolving in water and undergoing a hydrolysis reaction with
water. CO.sub.2(aq)+H.sub.2O H.sub.2CO.sub.3 (Equation 2)
where k forward -0.0025 to 0.04 s -t k reverse -10 to 20 s -1
This humble reaction controls the uptake of carbon dioxide by the
ocean because it is just slow enough to cause a significant mass
transfer limitation at the water's. Once the carbonic acid
(H.sub.2CO.sub.3) has formed it rapidly equilibrates to the species
shown in FIG. 1. The reverse reaction is the chemistry that
controls a human's exhaling carbon dioxide (dissolved in the
blood). Fortunately there is an enzyme, carbonic anhydrase, that
dramatically increases the speed of the reaction (in both
directions), permitting the dissolved carbonate to exit our lungs
as carbon dioxide. It is an extremely rapid converter of CO.sub.2
to H.sub.2CO.sub.3, with rates of up to 106 s-' in the form found
in human lungs. This is a speed up of 25 million above the
uncatalyzed reaction. Mass transfer limitations would appear to
restrict the overall speed up to perhaps a factor of 1000 before
the air transfer becomes limiting.
A second, and much faster reaction is also prominent when a lot of
hydroxide is present: CO.sub.2(aq)+OHHC0.sub.3.sup.- (Equation
3)
Where k forward -8.5.times.103 M'''s''r k reverse
-2.times.10.sup.-4 s'a
As is typical of this type of nucleophilic reaction, it is very
fast, and the rate is a direct function of the hydroxyl
concentration. FIG. 1 shows that this concentration becomes
overwhelming above pH 10 where the amount of hydroxyl available
then dominates the kinetic behavior. However even with a
dramatically faster conversion of CO.sub.2 to ionized species, the
mass transfer limitation is not easily overcome (more than another
factor of 10 in reaction speed would be required at 25.degree. C.
for the overall rate to be substantially affected by hydroxyl
concentration at pH=10. Thus very basic solutions are required for
the chemistry to enhance the overall absorption rate. The reverse
reaction is not dependant on hydroxyl concentration however, and is
relatively slow. This permits us to further refine the previously
defined regions:
Region 2A. pH 5-10: uptake of carbon dioxide is slow due to mass
transfer limitations. Carbonic anhydrase is critical for natural
systems to function in this pH range.
Region 2B. Above pH 10: direct attack of OH' on dissolved carbon
dioxide gas results in rapid uptake.
The small molecule catalysts Applicants have identified carbon
sequestering catalysts 3 and 4 nitrogen macrocycles with different
functional groups attached. Applicants have focused on 4 metals,
zinc, cobalt, copper and iron, for the metal centers. Also, the
benzimidizole compound provides protection to the metal from
becoming polluted. Formulas for three and four nitrogen macrocycles
with different functional groups and metals are below.
##STR00001## where R=H, S03.sup.-2, PEG, (CH.sub.2)nCH.sub.3, OH,
(CH.sub.2)nOH and M=an, Co, Cu, Fe.
Formulas for Benzoimdizole macrocycle shown with different
functional groups and different metal centers are below.
##STR00002## where R H, SO.sub.3.sup.-2, PEG, (CH.sub.2)nCH.sub.3,
OH and M=Zn, Co, Cu, Fe.
Carbon dioxide (CO.sub.2) sequestration is an application of high
interest due to the pressing need to capture large-scale, megaton
quantities of CO.sub.2 from industrial processes or the atmosphere.
For this reason, catalysts that may facilitate this process can
have a great environmental impact. In nature, the zinc
metalloenzyme carbonic anhydrase II (CAII) hydrates CO.sub.2 to
carbonic acid extremely efficiently at ambient conditions. Several
small molecule mimics of CAII have been designed over the years in
order to study the reaction mechanism and attempt to capture this
reactivity. Quantum mechanical calculations of two of the most
efficient mimetics, 1,4,7,10-tetraazacyclododedacane and
1,5,9-triazacyclododedacane (both complexed with a Zn.sup.2+ or
Co.sup.2+ ion), were performed to predict the reaction coordinate
for CO.sub.2 hydration. These calculations showed that the ability
of the metal ion to maintain a tetrahedral geometry and to have
bicarbonate bind in a unidentate manner were key aspects for the
hydration reaction. The catalytic activity of the zinc complexes
was insensitive to coordination but coordination higher than four
caused product release to be unfavorable for the cobalt
complex.
In recent years a growing awareness of CO.sub.2 atmospheric levels
sparked interest in developing rapid ways to absorb carbon dioxide
from industrial gas streams. Most industrial separation processes
for CO.sub.2 involve a liquid in which the dissolved CO.sub.2
ionizes, greatly increasing its solubility and absorption rate. The
rate limiting step in such processes is well known to be the
formation of carbonic acid. The slow kinetics of this reaction also
hinders the uptake of carbon dioxide by the ocean and causes a
significant mass transfer limitation at the water's surface. This
mass transfer limitation also applies to industrial gas separations
and results in overall decreases in rate factors in excess of
1000-fold over that which could be obtained if the hydration of the
CO.sub.2 were not the rate-limiting step. Accelerating such
processes through the use of catalysts or enzymes would permit
smaller and less expensive separation processes to remove CO.sub.2
from industrial gas emissions and removal of CO.sub.2 from the
atmosphere.
In biological systems, the reversible hydration of CO.sub.2 to
bicarbonate occurs at a greater efficiency via catalysis by the
zinc metalloenzyme, carbonic anhydrase (CA). In humans, carbonic
anhydrase II (CAII) is the most efficient isoform with diffusion
limited kinetics. The reaction is catalyzed by zinc-hydroxide which
is formed when a water molecule coordinates to the zinc, thereby
lowering the water's pK.sub.a to .about.7. The reaction mechanism,
which follows ping-pong kinetics, occurs as two independent steps.
In step one, the zinc-hydroxide in the active site of CA attacks
CO.sub.2 to form bicarbonate which is subsequently displaced by a
water molecule.
In the second step, the zinc bound water loses a proton to a
catalytic histidine (His64 in human CAII) and finally into bulk
solvent (and buffer) to regenerate the zinc-hydroxide catalyst.
Deprotonation of the water is the rate-limiting step in carbonic
anhydrase. The extremely high hydration turnover of CO.sub.2 by
CAII is .about.10.sup.6 sec.sup.-1 at pH 9 and 25.degree. C. The
reverse reaction, dehydration of bicarbonate occurs when the
solution pH is below 7.
The X-ray crystal structures of many different CAs have been solved
and studied in great detail. Crystallographic studies of human CAII
show that the enzyme is a monomeric protein consisting of 260
residues. The binding site is shaped like a funnel, with the metal
center at the bottom. The coordination geometry of the catalytic
zinc is tetrahedral with three histidines (His94, His96, and
His119) and a water/hydroxide molecule chelating the metal. The
active site can be divided into a hydrophobic half necessary for
CO.sub.2 binding and a hydrophilic half involved in a hydrogen
bonding network of residues and water molecules for efficient
proton release. Other divalent metals (Cu.sup.2+, Hg.sup.2+,
Fe.sup.2+, Cd.sup.2+, Ni.sup.2+, Co.sup.2+ and Mn.sup.2+) can bind
to CAII, but only Co.sup.2+ has near wild-type activity
(k.sub.cat/K.sub.m=8.7.times.10.sup.7M.sup.-1s.sup.-1 for Zn.sup.2+
vs 8.8.times.10.sup.7 M.sup.-1s.sup.-1 for Co.sup.2+). Since
Zn.sup.2+ is a poor spectroscopic species, Co.sup.2+ has played an
important role in studying CA because not only does it utilize a
metal-hydroxide catalysis and have near wild-type activity but is
also spectroscopically active.
Despite the merits of CAII, current research into the use of
carbonic anhydrase for industrial CO.sub.2 capture has received
limited publication partially due to the difficulty of maintaining
viable enzyme in industrial processes. Trachtenberg et al use a
membrane-countercurrent system originally designed for spacecraft
use. Bhattacharya et al uses a spray system with carbonic anhydrase
in the spray. Azari and Nemat-Gorgani examined means of using the
reversible unfolding of the enzyme, caused by heat, to attach it to
more sturdy substrates for industrial use. Yan et al incorporated
single carbonic anhydrase molecules in a spherical nanogel and
report greatly improved temperature stability with only moderate
loss of activity. A more viable possibility is to use small
molecules that mimic the CAII catalytic activity. Creating such
mimetics requires incorporating key structural features from the
enzyme scaffold and avoiding possible degradation mechanisms of the
catalytic center. Fortunately, CA mimetics were developed to study
the enzyme's reaction mechanism, and several examples of small
molecule CA mimetics exist. They include, to varying degrees,
structural features of the enzyme. The most prominent feature is a
set of nitrogen electron donors that play the role of the enzyme
histidine sidechains. These nitrogen atoms may be part of an
imidazole group or as secondary amines, such as in
1,4,7,10-tetraazacyclododecane or 1,5,9-triazacyclododecane, which
chelate a metal ion. These two macrocycles when chelated with
Zn.sup.2+ are able to catalyze both the hydration of CO.sub.2 and
the dehydration of bicarbonate depending on the solution pH exactly
as CAII although with a more modest catalytic activity.
The hydration reaction of CO.sub.2 catalyzed by N3 and N4 chelating
Zn.sup.2+ and Co.sup.2+ was investigated using quantum mechanical
calculations. All calculations were carried out using the program
Gaussian03. Geometry optimizations were performed at the
B3LYP/6-311+G* level of theory. The catalytically active form of
cobalt in carbonic anhydrase is experimentally known to be a high
spin quartet (S=3/2); thus, calculations on the cobalt-containing
mimics were carried out with a fixed quartet multiplicity. Harmonic
frequency calculations were performed on all the structures to
characterize the stationary points. Transition states were
characterized by a single imaginary frequency. The calculated
zero-point energies (ZPE) were not scaled. To investigate the
effects of solvation on the hydration reaction, single point
calculations using the gas-phase geometries were carried out using
a conductor-like polarizable continuum model (CPCM) to approximate
solvent effects (water, .epsilon.=78.4). It has been shown that the
solvation free energies from single point PCM calculations using
gas-phase geometries from density functional calculations are in
reasonable agreement with values obtained from full optimizations.
All solvation calculations used the simple united atom topological
model (UA0) using UFF radii. Natural population analysis was
performed on the optimized structures to assess the charge
distributions on the complexes.
Example 1
Catalyst Assisted Solvent Systems
Separation of CO.sub.2 from a gas mixture can be accomplished using
catalyst modified solvent system with a catalyst produced in
accordance with the present invention. Most industrial process for
separating CO.sub.2 from gas mixtures utilize water/buffer as the
primary separation media. This is because water provides an
extremely large factor to separated carbon dioxide from
non-ionizable gases such as nitrogen and oxygen. The water contains
additives that serve to buffer the carbonic acid that forms upon
CO.sub.2 dissolution, and also to speed the CO.sub.2 dissolution
process. Typically those additives are amines although in some
processes hydroxides (such as NaOH) are used. In this example, the
buffering compounds are assisted through the use of a catalyst. The
dissolved, attached, embedded or fluid surface confined catalyst
speeds the uptake of CO.sub.2 by the buffered media. This solves a
significant challenge in the normal process of carbon dioxide
separation by facilitating the use of lower contact areas required
for CO.sub.2 removal and expanding the selection of the buffering
compounds which can lead to lower overall energy costs associated
with recovery.
The catalyst can be produced by developing preliminary information
regarding the catalyst for harvesting carbon dioxide from a gas
mixture, using the preliminary information to produce a template of
the catalyst for harvesting carbon dioxide from a gas mixture, and
using the template of the catalyst for harvesting carbon dioxide
from a gas mixture to produce the catalyst for harvesting carbon
dioxide from a gas mixture. The step of developing preliminary
information regarding the catalyst for harvesting carbon dioxide
from a gas mixture includes developing preliminary information
regarding a molecule having potential energy surfaces around a
metal center that will optimize reaction with carbon dioxide. The
step of using the preliminary information to produce a template of
the catalyst for harvesting carbon dioxide from a gas mixture
includes generating a selection of linking atoms to compose a
scaffold on the metal center that will optimize reaction with
carbon dioxide.
The step of developing preliminary information regarding the
catalyst for harvesting carbon dioxide from a gas mixture includes
using molecule mimics. Applicants have used small molecule mimics
of CAII in order to study the reaction mechanism and attempt to
capture this reactivity. Quantum mechanical calculations of two of
the most efficient mimetics, 1,4,7,10-tetraazacyclododedacane and
1,5,9-triazacyclododedacane (both complexed with a Zn.sup.2+ or
Co.sup.2+ ion), were performed to predict the reaction coordinate
for CO.sub.2 hydration. These calculations showed that the ability
of the metal ion to maintain a tetrahedral geometry and to have
bicarbonate bind in a unidentate manner were key aspects for the
hydration reaction. The catalytic activity of the zinc complexes
was insensitive to coordination but coordination higher than four
caused product release to be unfavorable for the cobalt
complex.
Applicants have examined CO.sub.2 hydration as catalyzed by
1,4,7,10-tetraazacyclododedacane and 1,5,9-triazacyclododedacane
(denoted N4 and N3, respectively) chelating both Zn.sup.2+ and
Co.sup.2+ to investigate the reaction mechanism of these two metals
and determine the cause for the difference in activity seen in
human CAII. The hydration reaction of CO.sub.2 catalyzed by N3 and
N4 chelating Zn.sup.2+ and Co.sup.2+ was investigated using quantum
mechanical calculations. All calculations were carried out using
the program Gaussian03. Geometry optimizations were performed at
the B3LYP/6-311+G* level of theory. The catalytically active form
of cobalt in carbonic anhydrase is experimentally known to be a
high spin quartet (S=3/2); thus, calculations on the
cobalt-containing mimics were carried out with a fixed quartet
multiplicity. Harmonic frequency calculations were performed on all
the structures to characterize the stationary points. Transition
states were characterized by a single imaginary frequency. The
calculated zero-point energies (ZPE) were not scaled. To
investigate the effects of solvation on the hydration reaction,
single point calculations using the gas-phase geometries were
carried out using a conductor-like polarizable continuum model
(CPCM) to approximate solvent effects (water, .epsilon.=78.4). It
has been shown that the solvation free energies from single point
PCM calculations using gas-phase geometries from density functional
calculations are in reasonable agreement with values obtained from
full optimizations. All solvation calculations used the simple
united atom topological model (UA0).sup.i using UFF radii. Natural
population analysis was performed on the optimized structures to
assess the charge distributions on the complexes.
Example 2
Methane Monooxygenase Catalyst
Conversion of methane to methanol can be accomplished using a
methane monooxygenase catalyst produced in accordance with the
present invention. Methane monooxygenase, or MMO, is an enzyme
capable of oxidizing the C--H bond in methane as well as other
alkanes. Methane monooxygenase belongs to the class of
oxidoreductase enzymes. There are two well-studied forms of MMO:
the soluble form (sMMO) and the particulate form (pMMO). The active
site in sMMO contains a di-iron center bridged by an oxygen atom
(Fe--O--Fe), whereas the active site in pMMO utilizes copper,
although some propose that pMMO also uses iron. Structures of both
proteins have been determined by X-ray crystallography; however,
the location and mechanism of the active site in pMMO is still
poorly understood and is an area of active research.
The methane monooxygenase catalyst is produced by developing
preliminary information regarding the methane monooxygenase
catalyst for conversion of methane to methanol, using the
preliminary information to produce a template of the, and using the
template of the catalyst to produce the methane monooxygenase
catalyst for conversion of methane to methanol. The step of
developing preliminary information regarding the methane
monooxygenase catalyst for conversion of methane to methanol
includes developing preliminary information regarding a molecule
having potential energy surfaces around a metal center that will
optimize reactions. The step of using the preliminary information
to produce a template of the methane monooxygenase catalyst for
conversion of methane to methanol includes generating a selection
of linking atoms to compose a scaffold on the metal center that
will optimize reactions.
Example 3
Oxygen Evolving Complex Catalyst
Water oxidizing can be accomplished using a oxygen evolving complex
catalyst produced in accordance with the present invention. The
oxygen evolving complex, (OEC) also known as the water-splitting
complex, is a water oxidizing enzyme involved in the photooxidation
of water during the light reactions of photosynthesis. Based on a
widely accepted theory from 1970 by Kok, the complex can exist in 5
states: S.sub.0 to S.sub.4. Photons trapped by photosystem II move
the system from state S.sub.0 to S.sub.4. S.sub.4 is unstable and
reacts with water to produce free oxygen. The OEC appears to have a
metalloenzyme core containing both manganese and calcium, with the
empirical formula for the inorganic core of
Mn.sub.4Ca.sub.1O.sub.xCl.sub.1-2(HCO.sub.3).sub.y.
The oxygen evolving complex catalyst can be produced by developing
preliminary information regarding the catalyst for water oxidizing,
using the preliminary information to produce a template of the
catalyst, and using the template of the catalyst to produce the
catalyst for water oxidizing. The step of developing preliminary
information regarding the catalyst includes developing preliminary
information regarding a molecule having potential energy surfaces
around a metal center that will optimize reactions. The step of
using the preliminary information to produce a template of the
catalyst for water oxidizing includes generating a selection of
linking atoms to compose a scaffold on the metal center that will
optimize reactions.
Example 4
Nitrogen Fixation Catalyst
Nitrogen fixation can be accomplished using a catalyst produced in
accordance with the present invention. Nitrogen fixation is the
process by which nitrogen (N.sub.2) is converted into ammonia. This
process is essential for life because fixed nitrogen is required to
biosynthesize the basic building blocks of life, e.g. nucleotides
for DNA and RNA and amino acids for proteins. Formally, nitrogen
fixation also refers to other abiological conversions of nitrogen,
such as its conversion to nitrogen dioxide.
The nitrogen fixation catalyst can be produced by developing
preliminary information regarding the catalyst, using the
preliminary information to produce a template of the catalyst, and
using the template of the catalyst to produce the nitrogen fixation
catalyst. The step of developing preliminary information regarding
the nitrogen fixation catalyst includes developing preliminary
information regarding a molecule having potential energy surfaces
around a metal center that will optimize reactions. The step of
using the preliminary information to produce a template of the
nitrogen fixation catalyst includes generating a selection of
linking atoms to compose a scaffold on the metal center that will
optimize reactions.
While the invention may be susceptible to various modifications and
alternative forms, specific embodiments have been shown by way of
example in the drawings and have been described in detail herein.
However, it should be understood that the invention is not intended
to be limited to the particular forms disclosed. Rather, the
invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the following appended claims.
* * * * *